The invention relates to display panels, and more particularly, to transflective display (LCD) panels with reflective layer structures.
As manufacturing costs decrease and quality improves, liquid crystal displays are increasingly employed in different products such as notebook computers, personal digital assistants (PDAs), mobile phones, clocks, and the like. Liquid crystal displays are passive luminous devices and can include a backlight unit for LCD devices.
Typically, LCD devices can be divided into several types according to their display methods. Some examples are reflective LCD devices, transmissive LCD devices, and transflective LCD devices. A reflective LCD device saves power and reduces manufacturing costs by reflecting light from the environment to display images. A transmissive LCD device comprises an LCD panel and an additional backlight unit for providing a light source to the LCD panel, leading to higher brightness and less restrictions on use. Additionally, a transflective LCD device, which combines features of the transmissive LCD device and the reflective LCD device, is used because it can reflect ambient light to render images. The transmissive LCD device can also use a backlight unit to actively generate light in a low light environment, such as indoors or at night.
FIG. 1 is a schematic diagram of a conventional transflective display panel 10. As shown in FIG. 1, the transflective display panel 10 comprises a substrate with a plurality of scan lines 12 arranged in a transverse direction, a plurality of data lines 14 arranged in a longitudinal direction perpendicular to the scan lines 12, and a plurality of pixels corresponding to an intersection of each scan line 12 and data line 14. Each pixel comprises a switch region 16 and a display region 18. In the transflective display panel 10, the switch region 16 comprises a thin film transistor, such as a polysilicon thin film transistor. The display region 18 can be covered by a reflective layer with a transmitting hole that forms a transmissive area 114 and a reflective area 115. Thus, ambient light can be reflected by the reflective layer to a display image. A backlight unit can provide an additional light source through the transmissive area 114 to assist image display in a low light environment.
FIG. 2 is a cross-section of the display region 18 along a line A-A′ in FIG. 1. As shown in FIG. 2, the transflective display panel 10 comprises a substrate 112 defined with the transmissive area 114 and the reflective area 115 thereon. In conventional fabricating processes for TFT display panels, an inter-layer dielectric (ILD) layer or a planarization layer 116 can be disposed on the substrate 112 to protect electric devices, such as the thin film transistor located in the switch region 16, on the substrate 112. A transmissive hole 118 is formed on the substrate 112 to expose the transmissive area 114.
According to conventional fabricating processes of transflective display panels, a transparent electrode layer and a reflective layer can be formed in different sequences. For example, a structure can be formed with the transparent electrode layer on top or with the reflective layer on top. Since the reflective layer and the transparent electrode layer have different work function, the structure with the reflective layer on top can produce flicker problems, therefore the structure with transparent electrode on top is used as it can provide work function identical, thereby avoiding flicker problems.
As shown in FIG. 2, an adhesion layer 120 and a reflective layer 122 are formed on the planarization layer 116 in sequence. Thereafter, a transparent electrode layer 126 is formed on the reflective layer 122. As previously described, the reflective layer 122 can reflect ambient light to render images. The adhesion layer 120 improves a bonding force between the planarization layer 116 and the reflective layer 122.
An etching process can be performed to pattern the reflective layer 122 and the adhesion layer 120 in the bottom of the transmissive hole 118 to expose the transmissive area 114 prior to formation of the transparent electrode layer 126. Thus, the light source from the backlight unit can transmit through the transmissive area 114.
Typically, the reflective layer 122 is an aluminum alloy and the adhesion layer 120 includes molybdenum (Mo). In the previously described etching process, the adhesion layer 120 has a larger etching rate than the reflective layer 122 due to material properties. This can result in an undercut phenomenon, shown for example as 123 in FIG. 2, to be present in an edge 124 of the adhesion layer 120 adjacent to the transmissive area 114. This can reduce step-coverage of the transparent electrode layer 126 and lead to the presence of a discontinuity region or a weak contact region when the transparent electrode layer 126 is formed thereon. Further, this can deteriorate the display performance of the transflective display panel 10. Thus, a new transflective display panel structure and a fabricating method thereof are desirable.